This invention relates to a method of and an apparatus for reducing vibrations of a car body of an automobile, which vibrations are caused by roughness due to irregular combustion during the idling of the engine.
In the field of automobile engine control, various kinds of techniques concerning the reduction of vibrations of a car body caused by fluctuation of engine torque have heretofore been proposed. For example, JP-B-62-31172 (1987) proposes a conventional technique for suppressing vibrations caused by periodic fluctuation of torque which occurs in a crankshaft synchronously with the expansion stroke of the engine. According to the technique, periodic increase of torque in the expansion stroke of an engine is detected, and a field current is applied to a field coil of an alternator at this torque-increasing time to increase the torque of the alternator which the engine bears as a load. The increase in torque of the alternator suppresses the periodic increase of torque of the engine thereby to reduce not only vibrations of the engine, but also vibrations of the car body.
Vibrations of a car body include irregular vibrations caused by roughness due to irregular combustion occurring during idling of an engine, in addition to such vibrations ascribed to periodic fluctuation of torque due to the expansion stroke of the engine.
The idling roughness, which is roughness occurring during idling, is apt to occur, for example, when a sudden change in engine load at high-speed traveling to idling takes place to make the combustion unstable, and when the increase in combustion pressure is not sufficient. Due to such roughness, the number of revolutions (r.p.m.) of the engine suddenly varies to a lower value. Consequently, the engine vibrates as if it is excited in the rolling direction. In the case where an engine is placed longitudinally of the car body as in front engine rear drive cars, vibration of the engine is transmitted to the chassis through the mounts to cause the car body to abnormally vibrate. The mechanism of occurrence of vibrations of a car body ascribed to roughness is different from that of the above-mentioned periodic vibration ascribed to the combustion in the engine, since the former vibration occurs irregularly. Therefore, such irregular vibration cannot be eliminated by conventional techniques for suppressing the fluctuation of the torque of the engine. The frequency of vibration of a car body ascribed to idling roughness is as low as 5-8 Hz. Therefore, in order to reduce such vibration by a mechanical system such as a dynamic damper, it is necessary to provide a damper having a very large size, and so reduction of the vibrations thereby is not practical.